The central purpose of the proposed research is the study of neuronal migration and cellular integration following transplantation of immature neocortex into neuron-deficient motor cortex of neonatal mice, as a model for possible future transplantation as treatment for perinatal injury to cerebral cortex. The studies proposed will directly expand and continue ongoing studies funded by an NICHD Clinical Investigator Award. We developed a novel model of selective neocortical injury using noninvasive laser illumination, proposed as a basis for directed studies of neocortical transplantation. Most studies of neural transplantation have dealt with "global" systems in which transplanted neurons could effect recovery in a paracrine fashion; there are many questions with these models of transplantation regarding possible modes of recovery. Neuronal transplantation in neocortex would necessitate specific migration and synaptic integration of grafted cells into positions within the neuronal network left vacant by degenerated neurons. Unfocused laser energy, at long wavelengths that penetrate through tissue without major absorption, can cause extremely selective, noninvasive, cell-specific damage to desired subpopulations of neocortical neurons in vivo. Neurons are targeted by retrograde incorporation of cytolytic chromophores which are activated by the laser energy. Intermixed neurons, glia, axons, blood vessels, and connective tissue remain intact. This selective neuronal injury will allow precise control over the anatomical substrate for transplantation of neocortical neurons. Preliminary results suggest preferential migration by grafted neurons to, and integration within, regions of selective neuron deficiency. Our model and associated novel methods to distinctly label host and graft tissue at the light- and electron-microscopic levels will allow unique studies of transplanted embryonic neocortical cells at the cellular and ultrastructural levels. Experiments of Specific Aim I will refine this model of selective neocortical injury by defining the effects of varying laser energy and chromophore concentration on the "host" environment for later transplantation experiments. Experiments of Specific Aims II, III, and V will study the effects of embryonic donor age and the dysgenetic mutation reeler on neuronal migration and integration at the LM and EM levels. Such integration is critical to the goal of returning function within the complex neocortex injured by a variety of dysgenetic or perinatal influences. We will study whether immature neurons migrate selectively to their appropriate positions in lesioned zones of host cortex, to test the hypothesis that transplanted neocortex will seek to restore normal cytoarchitectonics. Experiments of Specific Aim IV will involve noninvasive removal of transplanted neurons to make possible rigorous tests of their functional integration and performance. Information as a possible future therapy for developmental, perinatal, or degenerative neocortical injury associated with Mental Retardation. Similar paradigms could prove useful in transplantation studies involving other nervous system regions and degenerative diseases.